Fuel cells can be used as a power source in many applications. For example, fuel cells can be used in electrical vehicular power plants to replace internal combustion engines and in stationary applications to produce electrical power. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied to the cathode. PEM fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive solid polymer electrolyte membrane having the anode catalyst on one of its faces and the cathode catalyst on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements that serve as current collectors for the anode and cathode. The conductive elements contain appropriate channels and/or openings therein for distributing the fuel cells' gaseous reactants over the surfaces of the respective anode and cathode catalysts. A typical PEM fuel cell and its MEA are described in U.S. Pat. Nos. 5,272,017 and 5,316,871 issued respectively Dec. 21, 1993 and May 31, 1994 and assigned to General Motors Corporation.
The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells depending on the context. A plurality of individual cells are commonly bundled together to form a fuel cell stack. Each cell within the stack comprises the MEA described earlier. A group of adjacent cells within the stack is referred to as a cluster.
In PEM fuel cells, hydrogen (H2) is the anode reactant (i.e., fuel) and oxygen is the cathode reactant (i.e., oxidant). The oxygen can be either a pure form (O2) or air (a mixture of O2 and N2). The anode reactant is typically supplied to the fuel cell from a pressurized storage tank or from a fuel reformer. The cathode reactant can also be supplied to the fuel cell stack from a pressurized storage tank or can be drawn from the surrounding environment by use of an airmover.
The airmover typically consists of an electric motor and a compressor, either centrifical, mixed flow, blower or screw type. The airmover typically uses a high-voltage motor to drive the compressor. During normal operation of the fuel cell system, the high voltage power produced by fuel cell stack is used to drive the airmover and, thus, supply the fuel cell stack with the cathode reactant. During start-up of the fuel cell system, however, the fuel cell stack is not producing enough power and is unavailable to power the airmover. Furthermore, during a shutdown operation it may be desired to perform a purging operation using the airmover while the fuel cell stack is not producing sufficient power to power the airmover. Accordingly, there is a need to provide a power source to drive the airmover during start-up and/or shutdown of the fuel cell system.
In some fuel cell systems, a low voltage power supply, such as a 12-volt automotive battery, is available. Prior attempts to utilize the 12-volt battery for powering the airmover during start-up have used a separate low voltage motor, separate windings in an existing motor, or a 12-volt blower. These methods, however, have proven to be complex and/or result in the addition of extra components to the system that can add weight and/or take up valuable space.